Method of assembling dynamoelectric machine brushes

ABSTRACT

An end cap assembly for a direct current motor. The assembly includes a brush retainer supported by the end cap that engages spring biased brushes to maintain the brushes in a retracted position. When an armature shaft is assembled to the end cap a portion thereof engages the retainer to move it relative to the end cap to a position where the brushes now engage the commutator of the armature. The retainer becomes a part of the motor. The end cap is formed as a one-piece plastic part that carries metallic brush holders and a circuit breaker. The circuit breaker is connected to one of the brush holders and to a terminal by C-shaped clips.

This application is a division of application Ser. No. 074,387, filedSept. 10, 1979 and now U.S. Pat. No. 4,293,785 granted on Oct. 6, 1981.

This invention relates to brush rigging for a dynamoelectric machine andmore particularly to brush rigging for direct current motors.

One of the problems encountered in the assembly of a dynamoelectricmachine rotor to an end cap or end frame of a dynamoelectric machine,where the end frame carries spring biased brushes that in use engage acurrent collector of the rotor, is maintaining the brushes in aretracted position out of the way of the current collector device of therotor as the rotor shaft is inserted into a bearing in the end frame.

One known arrangement for maintaining the brushes of a dynamoelectricmachine retracted is disclosed in the U.S. Pat. No. 3,219,860 to Redicket al. In this patent a tool is inserted through an opening formed inthe end wall of an alternating current generator which passes into abrush holder and which engages the ends of spring biased brushes tomaintain them retracted during assembly of the shaft and slip rings tothe end frame of the generator.

Another arrangement for maintaining brushes retracted is disclosed inthe U.S. Pat. No. 3,493,802 to Barthruff et al. In this patent a deviceis inserted through openings in a brush carrier to maintain the brushesretracted. Other United States patents that relate to brush retractingdevices are the U.S. Pat. No. 3,628,075 to Dafler and Winkelmann U.S.Pat. No. 3,739,205.

In contrast to the brush retracting devices disclosed in theabove-referenced patents the present invention contemplates providing adynamoelectric machine end cap assembly wherein an annular brushretainer is fitted to the end cap assembly such that it engages theinner walls of spring biased brushes supported by the end cap tomaintain the brushes in a retracted position. When the rotor of thedynamoelectric machine is assembled to the end cap by axially insertingthe rotor shaft into an end cap bearing the brush retainer is engaged bya portion of the rotor assembly and is shifted by axial movement of therotor to a position such that the brushes no longer engage the retainerand as a result the brushes are forced into engagement with the currentcollector of the rotor. The rotor may be the armature of a directcurrent motor in which case the current collector is a commutator.

It accordingly is one of the objects of this invention to provide an endcap assembly for a dynamoelectric machine that has a plurality ofradially disposed spring biased brushes that are held in a retractedposition by a brush retainer that slidably engages the end cap and whichcan be shifted to a position wherein the brushes engage the currentcollector of a dynamoelectric machine rotor when the shaft is axiallyinserted into the end cap. The retainer remains in the dynamoelectricmachine end cap and becomes a part of the final assembled dynamoelectricmachine.

Another object of this invention is to provide a method of assembling anend cap to a rotor of a dynamoelectric machine wherein the brushes aremaintained in a retracted position by an engagement with an axiallyshiftable brush retainer that is slidably supported by the end cap andwherein the step of inserting the shaft of the rotor of thedynamoelectric machine into the end cap axially shifts the brushretainer out of engagement with the brushes to thereby permit thebrushes to slide into contact with a current conducting means of therotor.

Still another object of this invention is to provide an end cap assemblyfor a dynamoelectric machine which is adapted for high volume automatedassembly of dynamoelectric machines. In carrying this object forward theend cap assembly is comprised of a one-piece molded part to which areattached brush holders that form with the one-piece part brush holdingchambers for guiding the brushes in their radial movement. The brushholders are formed of a conductive material and have tabs that are bentover into contact with one end of a brush spring the opposite end ofwhich engages a brush. The spring serves the dual function of urging thebrushes into contact with the commutator of the armature and also servesas a conductor electrically connecting the conductive brush holder tothe brush thereby eliminating brush shunts. The brush holders arepreferably secured to the one-piece end cap by staking over portions ofthe end cap into engagement with the brush holders and at least one ofthe brush holders has an integral male terminal projecting through anopening in the end cap for connection to a female terminal. Another maleterminal that projects through the end cap is provided and it iselectrically connected to one end of a circuit breaker assembly. Thecircuit breaker assembly and the last-mentioned male terminal haveengaged flange portions to make an electrical connection therebetweenand are clamped together by a C-shaped clip.

IN THE DRAWINGS

FIG. 1 is an end view of an end cap assembly for a dynamoelectricmachine made in accordance with this invention;

FIG. 2 is a sectional view taken along line 2--2 of FIG. 1 andillustrating the position of the brush retainer when it is maintainingthe brushes in a retracted position;

FIG. 3 is a sectional view taken along line 3--3 of FIG. 1;

FIG. 4 is a sectional view taken along line 4--4 of FIG. 1 andillustrating on an enlarged scale a rib that engages the brush retainerwhen it is in the FIG. 2 position;

FIG. 5 is a view illustrating the shaft and commutator of thedynamoelectric machine armature as assembled to the end cap andillustrating the position of the brush retainer after assembly; and

FIG. 6 is an exploded perspective view illustrating the parts that makeup the end cap assembly shown in FIG. 1.

The brush holding arrangement of this invention is disclosed hereinafterfor use on a direct current motor of the type that has an armature thatincludes a commutator and a permanent magnet field comprised ofpermanent magnets carried by the frame of the motor. It is to beunderstood, however, that the brush holding arrangement can be used withvarious types of dynamoelectric machines that utilize brushes thatengage rotary current conductors such as a commutator.

Referring now to the drawings, the reference numeral 10 generallydesignates an end cap assembly for a direct current motor. This end capassembly carries brush holders and spring biased brushes and also aprotective circuit breaker, all of which is more fully describedhereinafter. The end cap assembly forms the end housing of the directcurrent motor and comprises a one-piece molded plastic end cap 12 whichis depicted in FIGS. 1 and 6. This end cap may be formed, for example,from a thermoplastic polyester insulating material and is molded to theshape illustrated in FIGS. 1 and 6.

The entire armature of the direct current motor has not been illustratedsince it is conventional. This armature includes an armature shaft 22that carries a commutator 23. The commutator can take various knownforms in which the commutator bars are connected to an armature windingthat is wound in slots formed on a laminated magnetic core carried byshaft 22 and the commutator may be of a type wherein the bars aresupported by a spool of insulating material carried by the shaft andwherein the bars have hooks or tangs connected to the armature winding.Commutators of this type are disclosed in the above-referenced DaflerU.S. Pat. No. 3,628,075 and in the U.S. Pat. No. 4,041,339 to Huber.

The end cap 12 of the direct current motor is secured to a housing (notillustrated) that extends axially therefrom and which encloses thearmature of the motor. This housing carries permanent magnets whichprovide the field for the motor and carries a bearing for supporting theopposite end of the armature shaft in a known manner.

As seen in FIG. 5, the end wall portion 14 of the end cap 12 is providedwith a bore that receives a cylindrical portion of a thrust plug 16 thatforms a thrust bearing for one end of the shaft 22 of the armature ofthe direct current motor. The thrust plug 16 is formed of a plasticbearing material, for example a lubricated polyamide-imide. In addition,the end cap 12 has a central bore 18 which is fitted with a sinteredbronze bearing 20. When the armature of the direct current motor isassembled to the end cap assembly 10 the shaft 22 of the armature isinserted into the bearing 20 and against the end of the thrust plug 16.

The end cap 12 carries the parts in the final assembly which are shownin the exploded perspective view of FIG. 6. A brush holder and terminaldesignated by reference numeral 24 is assembled to cap 12. This brushholder and terminal is formed of a metallic conductive material, such asbrass, and has three walls forming a U-shaped brush retaining structureand has an integral male terminal 24a. The brush holder and terminal 24further has integral tabs 24b and 24c which, as will be described, arebent over into contact with the end of a brush spring to retain thebrush spring. The brush holder and terminal 24 has a laterally extendingflange portion 24d which has an opening that receives a stud 26 formedintegral with the end cap 12 when the part 24 is assembled to the endcap 12. The stud 26 is bounded by a recess 27 that receives the portion24d. Further, the part 24 has a laterally extending flange 24e shown inFIG. 1 having an arcuately extending wall 24f which partiallyencompasses an integral stud portion 28 of the end cap 12 when part 24is assembled to the end cap. The male terminal 24a passes through a slot30 formed in the end cap 12 so that it is accessible to the exterior ofthe end cap 12 when the part 24 is assembled thereto. With the part 24assembled to the end cap 12 the stud 26 is headed or staked over intocontact with flange 24d to securely fasten the part 24 to the end cap12.

The end frame assembly 10 further includes a terminal generallydesignated by reference numeral 32 formed of a conductive metallicmaterial such as brass. This terminal has a male terminal portion 32awhich projects through another opening 33 formed in the end cap 12. Theterminal 32 has a flanged portion 34 which is electrically connected toa circuit breaker assembly generally designated by reference numeral 36in a manner to be described. Further, the terminal 32 is formed with anarcuately extending wall 32b which partially encompasses the right sideof the stud 28 as illustrated in FIG. 1 and an arcuately extending wall32c that partially encompasses end cap part positioning stud 48 whichhas a pointed end. The terminal 32 is assembled to the end cap 12 bypushing the male terminal 32a through an opening 33 in the end cap 12.The stud 28 is subsequently staked over the terminal 32 and the flange24e of part 24 to thereby secure both the terminal 32 and the right sideof the part 24 to the end cap 12. It is pointed out that the maleterminals 24a and 32a extend to the exterior of the end cap 12 and areadapted to be connected with a female terminal connector.

The end cap assembly has a motor protecting circuit breaker generallydesignated by reference numeral 36. This circuit breaker assemblyincludes a base plate portion 36a formed of electrically conductivematerial and extending therefrom is a flange 36b. The base portion 36acarries a bimetal strip 38 secured to another bimetal strip 40 whichcarries an electrical contact 42. The contact 42 engages a fixed contact44 supported by the base 36a and is electrically insulated therefrom byinsulating washers disposed on opposite sides of base 36a, one of whichis illustrated and designated as 36d. Insulating arrangements of thisgeneral type are disclosed in the U.S. Pat. No. 3,718,162 to Dafler etal. In addition, the circuit breaker 36 has a connector portion 46formed of electrically conductive material which is electricallyconnected to contact 44.

In assembling the circuit breaker assembly 36 to the end cap 12 theopening 36c, formed in the flange 36b, receives the part positioningstud 48 integral with the end cap 12 with the flange 36b overlapping theportion of terminal 32 bounding opening 32c . Further, the portion 36bhas an outwardly struck tang 36e which fits within a circular recess 50formed in the end cap 12. It should be noted that when the circuitbreaker assembly is assembled to the end cap one end of the base plateportion 36a engages the right side of flange 34 of the terminal 32 asshown in FIG. 1. The stud 48 is not staked over and serves to positionparts 32 and 36 during assembly to end cap 12.

The end of the base plate portion 32a is maintained in tight engagementwith the flange 34 by the C-shaped clip 52. This clip is formed of anelectrically conductive material, for example a brass material, and whenit is assembled, as shown in FIG. 1, the wall defining the slot 52atightly engages the flange 34 and one wall of the end of the baseportion 36a to clamp these parts together.

The lower end of the circuit breaker assembly 36 is connected to thebrush holder 54 which is formed of a conductive metallic material suchas brass. As is illustrated in FIG. 6, the brush holder 54 is generallyU-shaped and has apertured flange portions 54a and 54b. A connectorportion 54c extends from the apertured flange 54b. The brush holder 54further has integral tabs 54d only one of which is illustrated in FIG.6. The other tab portion is identical with tab 54d and is arranged liketab 24b of brush holder 24. In the assembly of the brush holder 54 tothe end cap 12 the integral end cap studs or projections 56 and 58 ofthe end cap pass through the openings formed in the flange portions 54aand 54b. The flanges are received in recesses formed in the end cap, oneof which is designated by reference numeral 59. The studs 56 and 58 arethen staked over such that material of these studs flows over theflanges 54a and 54b to securely fasten the brush holder 54 to the endcap 12. It can be seen, from FIG. 1, that the flange 54c engages theconnector portion 46 of the circuit breaker assembly 36. This connectorportion is maintained in tight engagement with the flange 54c whenanother C-shaped clip 60 is assembled such that the walls defining theslot 60a engage opposite sides of the flange 54c and the connector 46 tomaintain them tightly clamped together. The clip 60 is formed of anelectrically conductive material and may be of the same material as theclip 52.

When the brush holders 24 and 54 have been secured to the end cap 12they form a brush guiding and retaining chamber designated by referencenumeral 62 shown in the sectional view of FIG. 3. It is seen, from FIGS.3 and 6, that the end plate 12 has a radially extending groove 64bounded by two planar brush supporting surfaces 66 and 68. The planarsurface 68 merges into a slanted surface 70 and the planar surface 66merges into another slanted surface 72. The ends of surfaces 68 and 70are formed with ribs 74 and 76 (FIG. 6) which serve to help maintain abrush within the chamber 62 when the brush is assembled to the brushholder.

The end cap 12 has another radially extending groove 78, a pair ofplanar brush guiding surfaces 80 and 82, ribs 84 and 86 and slantedsurfaces, like surfaces 70 and 72, one of which is illustrated in FIG. 6and designated by reference numeral 85. The cross section of the lowerbrush retaining area, which has just been described, of the end cap isthe same as the upper portion which is illustrated in FIG. 3.

It is seen in FIG. 3 that the end cap 12 has grooves or channels 88 and90. Further, with reference to FIG. 6, it is seen that brush holder 24has portions 24g disposed on opposite sides of flange 24d. The brushholder 24 has portions 24h, one of which is visible in FIG. 6 which aredisposed on opposite sides of flange 24c shown in FIG. 1. When brushholder 24 is asembled to end cap 12, a pair of sections 24g and 24h fitinto channels 88 and 90 as depicted in FIG. 3. Further, the other pairof sections 24g and 24h fit into channels or recesses 91 and 93.

In a similar fashion, the brush holder 54 has four sections 54e, threeof which are visible in FIG. 6, that fit into channels formed in thelower end of end cap 12 which are the same as channels 88, 90, 91 and 93formed in the upper end thereof. These channels are identified byreference numeral 95.

The brushes for the dynamoelectric machine are designated by referencenumerals 96 and 98 which are formed of a suitable carbon-coppercomposition. Since the brushes are identical only the configuration ofthe brush 96 will be described in detail. The brush 96 has a centralsection 96a having four flat surfaces. Further, the brush 96 haschamfered or slanted surfaces 96b and 96c which are illustrated in FIG.3. It can be seen that the flat wall 96d of the brush 96 slidablyengages planar surfaces 66 and 68 of the end cap 12 whereas the slantedsurfaces 96b and 96c of the brush 96 respectively engage slantedsurfaces 72 and 70 of the end cap 12. The brush 96 further has anannular portion 96e of reduced cross section as compared to the centralportion 96a of the brush to form therewith a surface 96f which engages abrush spring. The end surface 96g of the brush 96 is concave or curvedto fit the annular surface of the commutator 23. Further, this concavesurface is slanted such that the portion of 96e that is located adjacentthe face 96h has a larger axial dimension than the portion facing theend face 96d. Putting it another way, the concave surface slants suchthat the axial extent of portion 96e is less over an area facing the endplate 12. The brush 96 has another cylindrical portion 96k which isidentical to 96e and which has an end surface 96m that engages thecommutator. The surface 96m is identical to surface 96g and the brushcan therefore be inserted into the brush holder in either direction.Further, due to the provision of the complementary slanted surfaces onthe brush and end cap 96b and 72 and 96c and 70 the brush can only beassembled to the brush holder in one rotative position. This ensuresthat the brush surface that engages the commutator will always beproperly oriented with respect thereto. The brush 98 is in all respectsidentical with brush 96 and therefore is not described in detail.

Each brush is spring biased into engagement with the commutator 23 bybrush springs designated by reference numerals 100 and 102 that areformed of beryllium copper wire. The brush springs serve the dualfunction of biasing a brush into engagement with the commutator of thedynamoelectric machine and form an electrical connection between a brushholder and a brush.

The end frame 12 carries a brush retainer 104 which is formed of aresilient plastic material, for example nylon. This retainer has acentral opening 106, annular portions 108 and 110 and two arcuatelyextending portions 112 and 114. The end wall 110a of portion 110 extendsaxially beyond the edges 112a and 114a of portions 112 and 114. Prior toassembly of the brush retainer 104 to the end cap 12 of the arcuateportions 112 and 114 flare outward slightly and are sprung back to aposition shown in FIG. 2 when the retainer is assembled to the end cap.When the retainer is assembled to the end cap the portions 112 and 114tightly engage annular portions of the end cap 12. The brush retainer104 is initially assembled to the end cap 12 by forcing the outer wallsof portions 112 and 114 into contact with the internal walls of integralears or flange portions 116, 118, 120 and 122 of the end cap 12. Theinternal walls, for example the inner wall 120a of ear or flange 120,merges smoothly into annular wall 124 of the end cap 12. This is truefor all of the inner surfaces of the four flanges or ears 116-122.Further, each inner wall of a flange or ear is provided with a rib 126which is shown in the enlarged sectional view of FIG. 4. This rib has anannular wall 126a which engages the end 108a of annular portion 108 ofthe brush retainer when it is assembled to the end cap 12. The rib 126further has surface 126b that slants as shown in FIG. 4. The ribs 126have a small radial dimension which may be, for example, approximately0.25 millimeters.

The method of assembling the brushes to the end cap 12 and forassembling the armature of the motor to the end cap 12 will now bedescribed. Assuming that the brush holders have been assembled to theend cap 12, the brush retainer 104 is press fitted to the internal wallsof the flanges 116-122 such that areas of the outer wall of portion 112engage, respectively, the inner walls of ears 116 and 118 and areas ofthe outer wall of portion 114 engage, respectively, the inner walls ofears 120 and 122. Further, the wall 108a of the retainer engages the ribwalls 126a. This assembled position of the brush retainer is illustratedin FIG. 2 and in this position the outer walls of portions 112 and 114tightly engage the inner walls of the ears. The brushes 96 and 98 arenow inserted into the brush holders from the outside. The brush springs100 and 102 are now inserted into the brush holders from the outsidesuch that one end of the brush spring encompasses a cylindrical portionof the brush for example 96e with the end of the spring engaging a flatsurface, for example 96f. The brush spring is now compressed and thetabs, for example tabs 24c and 24b, are then bent over to engage anopposite end of a brush spring. This can be accomplished by a tool whichengages the end of a spring and which has a pair of slots permittingaccess to the tabs for bending the tabs over as the spring is heldcompressed by the tool. In FIGS. 1 and 2 the tabs are shown bent intoengagement with one end of a brush spring and they now serve to retain abrush spring in its assembled position where it urges a brush radiallyinward. The inner ends of the brushes engage the brush retainer 104 tomaintain the brushes retracted. It will be observed, from an inspectionof FIGS. 1 and 6, that the end walls 113 and 115 of end cap 12 haveopenings 117 and 119 which permit the brushes and brush springs to bepassed therethrough during assembly of the brushes and springs into thebrush holders. At this point in the assembly of a direct current motorthe end cap assembly 10 has brushes installed and the brush retainer 104is maintaining the brushes in a retracted position. A number of theseend cap assemblies can be manufactured at one station or area of aproduction plant and stored for subsequent assembly to the armature ofthe direct current motor.

When it is desired to assemble an armature of the direct current motorto a completed end cap assembly 10, the armature shaft 22 is insertedthrough the opening 106 in the brush retainer 104 by relative axialmovement between the end cap 12 and armature shaft 22. Assuming the endcap assembly 12 to be in a fixed position the shaft 22 is axially movedtoward the bearing 20 so as to be eventually inserted therein and duringthis movement an end wall 23a of the commutator 23 will become engagedwith the end wall 110a of portion 110 of the brush retainer 104. As theshaft of the armature continues to move relative to the end cap to itsfinal assembled position within the core of bearing 20 it will push thebrush retainer from the position shown in FIG. 2 to the position shownin FIG. 5. Thus, the brush retainer will be slid past and over the theribs 126 and will be slid into the annular bore wall 124 to the positionshown in FIG. 5. As the outer walls of portions 112 and 114 of the brushretainer 104 move out of contact with the inner ends of brushes 96 and98 they will be forced into engagement with the commutator 24 by thebrush springs.

In the final position of the brush retainer 104, the wall 108a isslightly spaced from the annular bore wall 130. It of course will beappreciated that the relative dimensions of the parts must be such thatthe retainer is shifted out of contact with the brushes 96 and 98 whenthe end of the shaft 22 is fully inserted into the bearing 20. Thelength of shaft 22, between its end that engages thrust plug 16 and theend 23a of the commutator 23 and the length of commutator 23, is suchthat the brushes engage the commutator substantially midway its length.The brush retainer 104 remains in the direct current motor and thereforeforms a component part of the motor once the armature shaft has beenassembled to the end frame.

It should be noted that all that is required in order to shift the brushretainer 104 relative to the end cap and to the FIG. 5 position isrelative motion between the armature shaft and the end cap. Thus,instead of holding the end cap fixed and moving the armature shaft intothe fixed end cap it is possible to hold the armature fixed and move theend cap relative thereto in order to cause the brush retainer to beshifted from the position shown in FIG. 2 to the position shown in FIG.5. It will be appreciated that during the shiftable movement of theretainer 104 it is slidably supported by the inner walls of the end capand is tightly retained in the final position of FIG. 5 by the tightengagement between the arcuate portions 112 and 114 of the brushretainer and the internal annular bore wall 124.

In order to simplify the description of the invention it is pointed outthat the sectional view of FIG. 2 does not depict all of the parts ofthe end cap. Thus, the circuit breaker and various other elements havenot been depicted in FIG. 2 it being understood, however, that the brushretainer 104, in the FIG. 2 position, is engaging the inner walls ofears 116-122 and is in engagement with the ribs 126 as shown in FIG. 4.

As previously mentioned, the end cap is secured to a tubular motorframe. The particular end cap disclosed herein has a pair of walls 132and 134 which are adapted to engage the ends of a steel motor frame (notillustrated) which engages walls 113, 115, 136 and 138. This end framecan be secured to the outer walls of the end cap 12 by staking overtangs (not illustrated) of the frame to the rear wall of the end cap 12.

In regard to the brush springs 100 and 102 providing an electricalconnection between the metallic brush holders and the brushes, thetangs, for example tangs 24b and 24c, make an electrical connection tothe end of a brush spring. Moreover, certain of the sides of the brushsprings, when a brush spring is compressed, tend to engage an internalwall of the U-shaped portion of a brush holder to further provide anelectrical connection between a brush spring and a brush holder. This isdue to a slight bowing of a brush spring after assembly.

The end cap 12 has two axially extending semi-circular portions 140 and142 which are partially disposed about the C-shaped clips 52 and 60 whenthey are assembled to the end cap assembly.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A method of assembling arotor of a dynamoelectric machine having a current conducting meanssecured to rotate with the rotor shaft to an end cap assembly that hasbearing means for receiving the rotor shaft and has spring biasedbrushes engaging the current conducting means once the rotor shaft isassembled to the end cap, the steps comprising, placing a radially outerwall means of a brush retainer having a central opening into engagementwith internal wall means of said end cap whereby the retainer issupported by the end cap, assembling a plurality of brushes andassociated springs that are separate from said brush retainer to saidend cap with a radially inner end of each brush engaging said outer wallmeans of said brush retainer and with the springs urging each brushagainst the retainer, the retainer serving to maintain the brushes in aretracted position, inserting the shaft of said rotor through thecentral opening in said retainer and into the bearing means, and duringthe insertion of said shaft engaging a portion of said rotor with saidretainer to axially slide said retainer relative to said end cap alonginternal wall means of said end cap to a position out of engagement withsaid brushes whereby the brushes are spring biased into engagement withsaid current conducting means of said rotor.
 2. A method of assemblingan armature of a dynamoelectric machine having a commutator secured torotate with the armature shaft to an end cap assembly that has bearingmeans for receiving the shaft and has spring biased brushes engaging thecommutator once the armature shaft is assembled to the end cap, thesteps comprising, placing a radially outer wall means of a brushretainer having a central opening into engagement with internal wallmeans of said end cap whereby the retainer is supported by the end cap,assembling a plurality of brushes and associated brush springs that areseparate from said brush retainer to said end cap with a radially innerend of each brush engaging said outer wall means of said brush retainerand with the springs urging each brush against the retainer, theretainer serving to maintain the brushes in a retracted position,inserting the shaft of said armature through the central opening in saidretainer and into the bearing means, and during the insertion of saidshaft engaging an end portion of said commutator with an end portion ofsaid retainer to axially slide said retainer relative to said end capalong internal wall means of said end cap to a position out ofengagement with said brushes whereby the brushes are spring biased intoengagement with said commutator.